In the electronic industries, silver-palladium pastes have been widely used in thick film conductive circuits employed in screen printing. The objects of using silver-palladium alloys are to repress the migration from occurring when wiring is made by the use of silver alone, to raise the melting point of silver by adding palladium so that the conditions for using substrates at desired temperatures are applicable, and the like.
U.S. Pat. No. 4,776,883 discloses a process for the production of silver-palladium alloy fine powder comprising the steps of forming an acid solution containing silver and palladium as ions; adding hydrazine or a hydrazine compound to said acidic solution; forming reduction-separated silver-palladium alloy fine powders having an average particle diameter of 0.01-1.0 microns; and heat-treating said reduction-separated silver-palladium alloy fine powders at a temperature of 100.degree.-500.degree. C. in an inert atmosphere or in a vacuum, wherein said silver-palladium alloy fine powders have a specific surface area ranging from 13-20 m.sup.2 /g prior to said heat-treatment, which is reduced to about 5-10 m.sup.2 /g after said heat-treatment. As it is well known to those skilled in the art, the reduced specific area of the silver-palladium fine powders can prevent the occurrence of increased oil absorption, lowered oxidation resistance and other inconveniences, which are results of using silver-palladium powders having a large specific surface area when the silver-palladium powders are used in a circuit screen printing paint or paste.
The objects of the present invention are to provide a process for preparing uniform silver-palladium powders having a specific surface area lower than that of the prior art silver-palladium fine powders; eliminating the energy intensive heat-treating step of the prior art process and thus reducing the captial investment on the heat-treating equipment and the plant space for accommodating said heat-treating equipment.